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Allegheny River

Northwest PA
September 11-13, 2007


Fisheries Management staff from the Area 2 office in Tionesta and the Area 1 office in Linesville night electro-fished the Allegheny River for smallmouth bass on the evenings of September 11 – 13, 2007. We sampled the same three sites (East Brady, Kennerdell and President) that were sampled from 1991 through 1997, 2005 and 2006.

Smallmouth bass

We captured a total of 669 smallmouth bass, which is both the highest number and the highest catch rate since sampling was initiated. The catch rate for bass > 12 inches remained high (2nd all-time) and the catch rate for bass > 15 inches was the highest ever (See Tables 1 & 2 and Figure 1).

Table 1. Length/frequency distribution for Smallmouth Bass captured by night electrofishing the Allegheny River at East Brady, Kennerdell and President on the evenings of September 11, 12 and 13, 2007.

Length (in.) Catch
2 10
3 86
4 80
5 15
6 22
7 29
8 146
9 145
10 63
11 26
12 17
13 8
14 5
15 4
16 6
17 3
18 1
19 3
Total 669

Table 2. Comparison of Smallmouth Bass Catch Per Hour rates (CPH) for three sites on the Allegheny River.

  1991 1992 1993 1994 1995 1996 1997 2005 2006 2007
Total Catch 281 458 261 209 321 278 243 359 445 669
CPH Total 48/hr 127/hr 51/hr 41/hr 59/hr 87/hr 65/hr 86/hr 111/hr 193/hr
CPH >= 12” 1.5/hr 6.4/hr 2.5/hr 2.5/hr 1.6/hr 7.5/hr 4.8/hr 7.9/hr 13.8/hr 13.6/hr
CPH >= 15” 0/hr 0.8/hr 1.2/hr 0.4/hr 0/hr 1.3/hr 0.8/hr 2.9/hr 3.5/hr 4.9/hr

Figure 1

Smallmouth bass

Flows have been low and fairly stable this year and fishing has been good most of the summer. The fishing is pretty good now, but the future could be even brighter. If the large 2005 and 2007 year classes experience good survival, smallmouth bass fishing should improve in the middle Allegheny River over the next few years.

Quite often, biologists talk about strong and weak year classes and how these affect what anglers see on the water. How is a strong year class created? Obviously, the successful spawning of a large number of young is important in the production of a strong year class, but this is only the first step. During subsequent years, the environmental conditions for survival (water temperature, flow, water chemistry etc.) must be favorable for a significant number of these young to survive, they must avoid being eaten, and there must be sufficient forage for these fish to survive and grow to a size satisfactory to anglers. These processes are largely determined by environmental conditions and the 2005 and 2007 year classes of smallmouth bass in the middle Allegheny River are good examples of this dynamic process in action.

Smallmouth bass

Spawning

We conduct an annual survey in July of smallmouth bass spawning success by backpack electrofishing for young of the year (YOY) bass at established sites (Figure 2). This year reproduction was excellent as the 2007 index was the highest since our YOY sampling began in 1987. The 2005 index was the fifth highest.

Figure 2

* No YOY sampling in 2004.

Survival

Breaking down the 2007 catch of smallmouth bass by age (Figure 3) shows that the 2005 year class (Age 2+) is extremely large and constituted almost 60% of all smallmouth captured. The 2007 year class comprised almost 29% of the total catch and these small fish (2 – 4 inches) are usually under-represented in our night electrofishing samples because they don’t occupy the same habitat as the adults and they are more difficult to capture by boat electrofishing.

Figure 3

Growth

Anyone who fished the middle Allegheny River this year probably saw the same thing we did, which is that the amount of forage available for bass (and other predators) was outstanding. Apparently, the suckers, chubs, shiners and darters also experienced excellent reproduction and survival in 2007. Because of this dense forage base, the summer of 2007 was a good year for smallmouth bass growth. The average smallmouth bass born in 2005 grew 3.7 inches in 2005, only 2.2 inches in 2006, but then added 3.6 inches by September of 2007 with still more time to grow in 2007.

While the average size of a bass born in 2005 was 9.5 inches this year, the complete sample of the 2005 year class ranged in size from 7 to 12 inches. Only seven out of these 392 two year old bass were over 12 inches. If river conditions remain favorable, most of these 2005 fish should attain legal length sometime during the summer of 2008.

What’s this mean to the angler?

The 2005 year class started with a high number of young. Then flow and forage conditions allowed this year class to exhibit good survival through 2006 and 2007. One more year of favorable conditions and they will start to make a sizable contribution to the number of legal smallmouth bass in the middle Allegheny River, something anglers should be able to see in their catches. We anticipate that anglers will see increased catch rates from the 2005 year class for several years.

The 2007 year class is off to a good start, but these fish must survive what can be a harsh environment for young fish. If they are to contribute to the Allegheny River fishery, they need the positive environmental conditions similar to those that allowed the 2005 year class to flourish. Future samples will tell us how they fare.

While the target of our sampling was smallmouth bass, we also counted 149 young of the year walleye, which is the highest ever. Similar to the smallmouth bass, walleye produced a good year class in 2005 and an outstanding year class in 2007.

Young of year walleye
A young of the year walleye

 
-- Tim Wilson, Area 2 Fisheries Biologist

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